In the heat treatment of textiles, carpet, and the like, dryer ovens are utilized which include a heated insulated chamber through which cloth is passed to dry, finish or set the cloth. The air in the dryer must be steadily or frequently replaced at an adequate rate to carry away moisture evaporated from the cloth in drying or to carry away smoke or lint generated from the cloth in a finishing or setting operation. In practice, the air in the dryer is replaced with fresh makeup air at the rate of ten to twenty tons of air per hour. This air usually enters the dryer at room temperature and is exhausted from the dryer at temperatures of about three hundred degrees Fahrenheit. The heat required to elevate the temperature of the replacement air from room temperature to three hundred degrees requires one to two million BTU's per hour of heat energy which constitutes anywhere from forty to sixty percent of the heat used to operate the dryer.
It has been proposed to provide an air-to-air heat exchanger mounted to a textile dryer oven wherein the exhaust is passed in heat exchange relationship with the replacement air. However, such involves passing exhaust and makeup air in opposite directions through separate paths in the heat exchanger continuously in opposite directions requiring upkeep in maintaining a filter system and the heat exchangers clean and free of lint, smoke, and oil resulting from the heat treatment process. Such is also the case in U.S. Pat. No. 3,712,597 wherein a series of bayonet type metallic recuperative heat exchangers are utilized in combination with a continuous rotary regenerated air preheater in a glass manufacturing oven. The plugging and cleaning problems created by lint, oils and resins exhausted from textile dryers are a major deterent to the use of heat exchangers on textile dryers.
In accordance with the present invention, exhaust heat recovery and replacement air preheating apparatus includes a pair of heat recovery and storage units installed in the walls of the dryer oven so that hot air exhausted from the dryer passes through one of the heat recovery and storage units wherein most of the heat energy is recovered by a plurality of heat absorbing elements. Cool replacement air simultaneously enters the dryer through the other of the heat recovery and storage units which has previously been heated by the exhaust whereby the replacement air is preheated. As a result, fresh replacement air is heated nearly to the dryer temperature before it enters the oven and exhaust air is cooled to approximately 130 to 160 degrees Farenheit before being released to the ambient atmosphere. The heat previously required to heat the replacement air is substantially reduced and the fuel required to operate a dryer oven can be cut almost in half.
The heat storage means are stationary. The heat storage end near the dryer is hot, the other end near the valve is cool. The exhaust carries two kinds of contamination which in combination plug heat exchangers. Lint made of fine fiber or dust will plug exchangers if the flow is continuous in direction. With this invention the reversing flow direction back flushes lint out of the heat storage before it passes the hot end so it does not plug or move through with smoke to the cool end. The second contamination in the exhaust is smoke consisting of volatized oil and resin from cloth in the dryer. Volatized oil and resin will condense when it contacts cool surfaces. It passes as gas through the hot storage end and condenses at the cold end but the lint has been separated out so build up on surfaces is minimal. The invention structure permits removal of the stationary storage elements at the cold end for simple periodic cleaning without interrupting dryer production. Thus, condensed oil and resin buildup can be held at operational levels. The heat of exhaust is effectively prevented from reaching the ambient environment and the ducts remain relatively cool eliminating the need for costly insulation.